Jupiter Flight Jeopardized by Failure to Free Antenna : Space: Odds increase that $1.4-billion Galileo mission will be unable to transmit data on the distant planet.
The latest attempt to free the stuck antenna on the Jupiter-bound Galileo spacecraft has failed, placing the $1.4-billion mission in dire jeopardy.
Engineers at the Jet Propulsion Laboratory in Pasadena had hoped to use the coldness of space to chill and shrink part of the antenna, thus freeing three stuck ribs. But by Tuesday morning it had become clear that scientists had fallen short in their strongest effort so far to fix the device.
“It’s a disappointment,” said project manager William O’Neil, but he said the technique will be tried again in December when Galileo will be even farther from the sun--and thus colder--than it is now.
The $3.7-million, gold-plated antenna is designed to open like an inverted umbrella, and it must be fully opened for Galileo to send back the thousands of photographs and reams of scientific data it is to collect during a two-year tour of Jupiter and its moons beginning in 1995. Without the 16-foot-wide antenna, all but a tiny amount of that priceless data, and all of the photographs, will be lost.
Engineers believe their latest effort may have failed because they missed their desired temperature by only a few degrees and could not get the craft colder than minus-238 degrees Fahrenheit.
Those who have been working on the Galileo project for more than a decade will watch a large chunk of their lives disappear into space with the 2 1/2-ton spacecraft if the antenna cannot be opened. While there is still time to work on the problem, the odds of success are worsening.
Scientists are in a Catch-22 predicament in that they need the antenna to be especially cold to free the stuck ribs, but they need it to be relatively warm for the motors that drive the ribs to operate at maximum efficiency.
If the ribs are still stuck in December, 1992, it may be too late to solve the problem because Galileo will enter its final course toward Jupiter, growing colder with each passing day. So while the ribs may finally free up, the motors may be too weak to push the antenna open.
The problem was discovered April 11 when engineers at the Pasadena lab, which is managed by Caltech for the National Aeronautics and Space Administration, turned on the motors that drive the ribs out from a central column. Three of the 18 ribs remained stuck, forcing the parabolic antenna into a claw-like shape.
Engineers determined that movement of the stuck ribs had been restricted by pins designed to guide them as they opened. In May, the spacecraft was turned so that the sun struck the ribs, in the hope that a little warmth would free them. But that failed to do the job.
In June, Galileo was turned so that the antenna was in the shadow of the spacecraft for 32 hours because engineers believed that a drop in temperature would cause the central column to shrink. That could allow the ribs to slide into their open position.
That failed, so engineers decided to leave Galileo out in the cold for a longer period. Last week the antenna was shaded for 50 hours and some instruments were turned off, in hopes of plunging the column’s temperature down to minus-274 degrees Fahrenheit.
Engineers believe that if they can reach that temperature the column will shrink about 80 thousandths of an inch, reducing friction and allowing the ribs to deploy.
Unfortunately, O’Neil said, the temperature reached only minus-238 degrees, 36 degrees too warm.
“I would be really disappointed if we had reached that temperature and it still had not worked,” he said, because that would suggest that the basic strategy is wrong.
The scientists will try again this December, when the spacecraft will be at its coldest point for the next year.
Theoretically, engineers can continue to alter the temperature for years in hopes of freeing the antenna.
Although extremely cold temperatures could free the ribs, O’Neil said, the motors that push the ribs out operate the most efficiently when they are much warmer. And after Galileo zips past Earth and heads out toward Jupiter in December, 1992, the spacecraft will never again be very warm.
Galileo seems to have been jinxed from the very beginning. It was scheduled to have been launched years ago, but was delayed by various problems, including the explosion of the space shuttle Challenger. After that disaster, the mission had to be redesigned to allow Galileo to be launched from the space shuttle with a safer but less powerful propulsion system than had been planned.
For a while, NASA executives considered abandoning the program entirely, but on Oct. 18, 1989, Galileo was launched from the space shuttle Atlantis. But Galileo’s less powerful rockets required the spacecraft to follow a twisted course to Jupiter, using the gravitational force of Venus and the Earth to accelerate it along the way.
After it was finally launched, everything seemed to be working perfectly for the spacecraft, but that took a dramatic turn on April 11 when the antenna refused to open.
No matter what happens now, scientists will get at least something for their efforts. Galileo is to fly past the asteroid Gaspra on Oct. 29, and a smaller antenna on the spacecraft will be able to send back some of the data from that historic encounter.
But if the antenna cannot be fixed by the time the craft reaches Jupiter in 1995, Galileo will fail to reach the objectives of its primary mission. The mission, and the efforts of scores of scientists and engineers who have devoted years to the Galileo project, will be lost.
Galileo in Trouble
The third effort to free the 16-foot antenna on the Jupiter-bound Galileo spacecraft has failed. Engineers believe at least one of the ribs in the antenna, which opens like an inverted umbrella, is stuck. The antenna must open fully to transmit most of its scientific data and photographs of Jupiter to Earth.
Engineers had hoped that chilling the antenna would free its stuck ribs, so they turned it away from the sun for 50 hours. But the procedure did not work, leaving the $1.4-billion mission in jeopardy.
This is the way Galileo should look, with its antenna fully open.
Source: Jet Propulsion Laboratory
